This invention pertains to refractory shapes such as brick and particularly to such shapes having a resin bond.
Carbon bonded refractories, particularly those containing basic aggregate such as periclase, have come into widespread use in recent years.
It has been discovered that refractories containing carbon are protected by their carbon content so that they do not wear as rapidly in a steelmaking environment as similar refractories not containing carbon.
Formerly, such carbon containing refractories were made with tar or pitch as a binder, but there were problems because tar bonded brick had to be made at elevated temperatures (where the tar or pitch was liquid) and subsequently heated to even higher temperatures to "cure" or harden the bond so the brick could be handled, as for shipping or installing. See, for example, U.S. Pat. Nos. 4,184,883 and 4,558,019.
Resin bonds obviate some of these problems. For example, resin bonds can be liquid at room temperature and therefore a refractory mix with a resin bond does not need to be heated in order to form brick. See, for example, U.S. Pat. Nos. 4,216,020 and 4,306,030.
However, the use of resin bonds introduced other problems. One big problem is that it is hard to achieve the desired density, and consequent strength and other properties, with a resin bond. This is apparently because it is very difficult to remove the air through the viscous resin when the refractory mix is pressed.
It has been found that adequate density (and strength) can be obtained in such brick if, in pressing the brick, the refractory material in the die box of the press is subjected to a series of maximum or elevated pressures alternated with lowered pressure on the press. The maxima in this pressure cycle are often referred to as "impacts", the number of impacts being the number of applications of maximum or elevated pressure separated by lowered pressure.
In the past it has been necessary to apply up to 15 or more impacts to a resin bonded brick to achieve the desired density. Furthermore, it has been found that the increase in density with number of impacts is not linear, but that there is a levelling off of density with increased number of impacts. In other words, no matter how many impacts are applied to the brick, it never reaches more than an asymptotically approached maximum density.
It will be evident to those skilled in the art that the necessity for applying multiple impacts to resin bonded brick to achieve the required density makes for a relatively slow and therefore expensive pressing operation.
The present invention overcomes or at least greatly reduces this problem and enables more rapid production of resin bonded brick. Briefly, with the use of the present invention, not only can a given, desired density (and consequent strength) be obtained in a brick with fewer impacts during pressing, but in addition it is possible, if desired, to reach a higher ultimate density (and strength). In other words, when the present invention is used, the curve of density vs. the number of impacts rises faster and reaches a higher ultimate density than with prior art methods and compositions. This ability to achieve a desired density is referred to herein as "pressability".